Machine Devices
A machine safety device is any tool or system designed to protect workers by preventing contact with dangerous parts of a machine.
Types of Safeguarding Devices
Devices help control or stop the machine's operation if a hazard is detected, or they create a physical barrier between the operator and the danger area. These devices must reduce the risk of accidents and ensure safer working conditions around machinery.
What Do Safeguarding Devices Do?
- Stop or control the machine if a hazard is detected
- Create a barrier between the worker and the danger zone
Types of Safeguarding Devices
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Presence-Sensing Devices: Use light curtains, lasers, or pressure-sensitive mats to detect a worker’s presence. If someone enters the danger area, the machine stops automatically.
Example: A light curtain around a robotic arm that shuts the machine off if a hand breaks the beam. -
Pullback Devices: Use cables or straps attached to a worker’s hands or arms. As the machine begins operating, it pulls the worker's hands away from the danger zone.
Example: A pullback system on a mechanical press. -
Restraint Devices: Keep the operator’s hands in a safe zone by using straps or devices that limit movement.
Example: A fixed strap system that prevents the worker’s hands from reaching into a cutting area. -
Safety Trip Controls: Include bars, ropes, or wires that stop the machine when pressed or pulled.
Example: A tripwire across the front of a conveyor belt that stops it if a worker stumbles into the area. -
Two-Hand Controls: Require both hands to be on controls to keep them away from dangerous parts during machine operation.
Example: A two-button press that must be held down with both hands for the press to operate. -
Gates: Physical barriers that move into place when a machine operates, preventing access to dangerous parts.
Example: A sliding gate that closes before a cutting blade moves.
- Presence-Sensing Devices
- Light Curtains: Infrared beams that detect intrusion into hazardous areas, halting the machine if interrupted.
- Laser Scanners: Scan areas for unauthorized presence and stop operations if detected.
- Pressure-Sensitive Mats: Trigger machine stoppage when footsteps or weight are detected in restricted zones.
- Safety Edges: Pressure-sensitive strips that stop machinery upon contact.
- Emergency Stop Devices
- Push-Button E-Stops: Red buttons with yellow backgrounds for immediate machine shutdown.
- Pull-Cord Switches: Cables along conveyors or machines that stop operation when pulled.
- Foot-Operated E-Stops: Foot-activated switches for hands-free emergency stopping.
- Two-Hand Control Devices
- Require simultaneous use of both hands to operate, keeping hands away from hazardous areas.
- Pull-Back Devices
- Designed to withdraw the operator's hands from the point of operation during the machine cycle.
- Restraint Devices
- Designed to physically prevent the operator’s hands or body from entering hazardous areas of a machine.
- Anti-Tie-Down Controls
- Prevent bypassing two-hand controls by requiring simultaneous activation.
- Interlock Switches
- Mechanical Interlocks: Prevent machine operation unless guards or doors are closed.
- Non-Contact Interlocks: Use magnetic or RFID technology for secure, contactless safety.
- Trapped Key Systems: Require a key to unlock or operate machinery, ensuring safe sequential access.
- Safety Relays and Controllers
- Monitor safety circuits, ensuring devices like E-stops or light curtains function correctly and stop the machine if faults occur.
- Safety Limit Switches
- Detect component position or movement, stopping operation if limits are exceeded.
- Safety Sensors
- Proximity Sensors: Detect objects or personnel near hazardous areas.
- Temperature/Pressure Sensors: Monitor unsafe conditions to prevent accidents.
- Enabling Devices
- Handheld devices that allow machine control only when actively engaged, stopping if released.
- Safety PLCs (Programmable Logic Controllers)
- Specialized controllers managing complex safety functions and integrating multiple devices.
- Time-Delay Devices
- Ensure machines stop after a safe interval to avoid sudden halts that could create hazards.
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3-1. What is the main purpose of a machine safety device?
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